Improvements relating to wind turbines

Abstract

The present invention relates to a method and to a wind turbine for determining the tip angle of a blade of a wind turbine rotor during rotation of the rotor. The method comprising: (a) transmitting a light signal from a first blade of the wind turbine rotor towards a second blade of the rotor; (b) receiving the light signal at the second blade of the rotor; and (c) calculating the tip angle of the first or second blade based upon characteristics of the received light signal.

What is claimed is: 
     
       1. A method of determining the tip angle of a blade of a wind turbine rotor during rotation of the rotor, the method comprising:
 (a) transmitting a light signal from a first blade of the wind turbine rotor towards a second blade of the rotor; 
 (b) receiving the light signal at the second blade of the rotor; and 
 (c) calculating the tip angle of the first or second blade based upon characteristics of the received light signal. 
 
     
     
       2. The method of  claim 1 , wherein step (a) comprises transmitting the light signal from a transmitter located near the tip of the first blade. 
     
     
       3. The method of  claim 2 , further comprising communicating light to the transmitter from a remotely-located light source via a first optical fibre extending longitudinally along the first blade. 
     
     
       4. The method of  claim 1 , wherein step (b) comprises receiving the light signal at a receiver located near the tip of the second blade. 
     
     
       5. The method of  claim 1  further comprising communicating the received light signal to a remotely-located detector via a second optical fibre extending longitudinally along the second blade. 
     
     
       6. The method of  claim 1 , wherein:
 step (a) comprises transmitting first and second substantially identical light signals respectively from first and second transmitters, the first and second transmitters being located near the tip of the first blade and spaced apart in the chordwise direction of the first blade; and 
 step (c) comprises calculating the tip angle of the first blade. 
 
     
     
       7. The method of  claim 6 , wherein step (c) comprises determining the optical path difference between the first and second signals and using the optical path difference to calculate the tip angle. 
     
     
       8. The method of  claim 6 , wherein:
 step (a) comprises continuously varying the frequency of the transmitted light signal from a first frequency to a second frequency; 
 step (b) comprises detecting a blinking interference signal caused by constructive and destructive interference occurring between the first and second light signals as the frequency is varied between the first and second frequencies; and 
 step (c) comprises calculating the blade tip angle based upon characteristics of the interference signal detected in step (b). 
 
     
     
       9. The method of  claim 8 , wherein step (c) comprises counting the number of blinks that occur in the interference signal when the frequency is varied from the first frequency to the second frequency and calculating the blade tip angle based upon the counted number of blinks. 
     
     
       10. The method of  claim 8 , wherein step (c) comprises determining the blinking frequency of the interference signal and calculating the blade tip angle based upon the blinking frequency. 
     
     
       11. The method of  claim 1 , wherein:
 step (b) comprises receiving the transmitted light signal at first and second receivers, the first and second receivers being located near the tip of the second blade and spaced apart in the chordwise direction of the second blade; and 
 step (c) comprises calculating the tip angle of the second blade. 
 
     
     
       12. The method of  claim 11 , further comprising converting the received light signal into first and second substantially identical light signals. 
     
     
       13. The method of  claim 1 , wherein:
 step (a) comprises transmitting a spectrum of light from the first blade towards the second blade; 
 step (b) comprises receiving one or more frequencies of the spectrum of light at the second blade; and 
 step (c) comprises calculating the tip angle based upon the frequency of the detected light. 
 
     
     
       14. The method of  claim 13 , wherein the respective frequencies spread out spatially moving from the first blade towards the second blade. 
     
     
       15. The method of  claim 13 , wherein step (a) further comprises forming the spectrum of light by refracting white light using refracting means such as a prism. 
     
     
       16. The method of  claim 1 , further comprising:
 transmitting light from a plurality of transmitters spaced apart along the length of the first blade and/or receiving transmitted light at a plurality of receivers spaced apart along the length of the second blade; and 
 determining the twist and/or load along the first blade on the basis of characteristics of the received light. 
 
     
     
       17. The method of  claim 16 , wherein the light from each transmitter is received by the same receiver. 
     
     
       18. The method of  claim 16 , wherein each transmitter transmits light having a unique frequency or a unique range of frequencies that is different to the frequencies transmitted by the other transmitters. 
     
     
       19. The method of  claim 16 , wherein each transmitter transmits light having a unique polarisation that is different to the polarisation of light transmitted by the other transmitters. 
     
     
       20. A wind turbine comprising:
 a rotor having a plurality of blades; 
 a light source; 
 a transmitter provided on a first blade of the rotor, the transmitter being arranged to transmit a light signal from the light source towards a second blade of the rotor; 
 a receiver provided on the second blade, the receiver being arranged to receive the light signal transmitted from the first blade; 
 a detector for detecting the received light signal; and 
 a processor in communication with the detector and arranged to calculate the tip angle of the first or second blade based upon characteristics of the detected light signal. 
 
     
     
       21. The wind turbine of  claim 20 , wherein the transmitter comprises one or more lenses for directing the light signal towards the receiver, and the receiver comprises one or more lenses for receiving the light signal. 
     
     
       22. The wind turbine of  claim 20 , wherein the light source is located remotely from the transmitter, and the wind turbine further comprises a first optical fibre extending longitudinally along the first blade between the light source and the transmitter. 
     
     
       23. The wind turbine of  claim 20 , wherein the detector is located remotely from the receiver and the wind turbine further includes a second optical fibre extending longitudinally along the second blade between the detector and the receiver. 
     
     
       24. The wind turbine of  claim 20  comprising first and second transmitters located near the tip of the first blade and spaced apart in the chordwise direction of the first blade, the first and second transmitters being arranged respectively to transmit first and second substantially identical light signals towards the receiver on the second blade, wherein the first and second light signals interact to form an interference signal. 
     
     
       25. The wind turbine of  claim 24 , wherein the first transmitter is located substantially at the leading edge of the blade and the second transmitter is located substantially at the trailing edge of the blade. 
     
     
       26. The wind turbine of  claim 24 , wherein the first optical fibre branches into first and second secondary optical fibres associated respectively with the first and second transmitters. 
     
     
       27. The wind turbine of  claim 26 , wherein the first optical fibre branches at a point close to the tip of the first blade. 
     
     
       28. The wind turbine of  claim 20 , comprising first and second receivers located near the tip of the second blade and spaced apart in the chordwise direction of the second blade. 
     
     
       29. The wind turbine of  claim 28 , wherein the first receiver is located substantially at the leading edge of the blade and the second receiver is located substantially at the trailing edge of the blade. 
     
     
       30. The wind turbine of  claim 28 , wherein the first and second receivers are arranged to convert the received light signal into first and second light signals which interact to form an interference signal. 
     
     
       31. The wind turbine of  claim 20 , wherein the frequency of light emitted by the light source can be varied between a first frequency and a second frequency. 
     
     
       32. The wind turbine of  claim 31 , wherein the interference signal comprises a series of flashes caused by constructive and destructive interference occurring between the first and second light signals when the frequency of the transmitted light signal is varied from a first frequency to a second frequency. 
     
     
       33. The wind turbine of  claim 32 , wherein the processor is configured to determine the blade tip angle on the basis of a determined optical path difference between the first and second signals. 
     
     
       34. The wind turbine of  claim 32 , wherein the processor is configured to determine the blade tip angle on the basis of a counted number of flashes associated with the interference signal when the frequency of the transmitted light is varied from the first frequency to the second frequency. 
     
     
       35. The wind turbine of  claim 32 , wherein the processor is configured to determine the blade tip angle on the basis of the frequency of flashes associated with the interference signal when the frequency of the transmitted light signal is varied from the first frequency to the second frequency. 
     
     
       36. The wind turbine of  claim 20 , wherein:
 the transmitter is arranged to transmit a spectrum of light from the first blade towards the second blade; 
 the receiver is arranged to receive one or more frequencies of the spectrum of light at the second blade; 
 the detector is arranged to detect the frequencies of the received light; and 
 the processor is configured to calculate the tip angle based upon the frequencies of the detected light. 
 
     
     
       37. The wind turbine of  claim 36 , wherein the transmitter is configured to cause the respective frequencies to spread out spatially moving from the first blade towards the second blade. 
     
     
       38. The wind turbine of  claim 36 , wherein the light source is a source of white light and the transmitter comprises a prism for refracting the white light to produce the spectrum of light. 
     
     
       39. The wind turbine of  claim 20 , further comprising a plurality of transmitters spaced apart along the length of the first blade. 
     
     
       40. The wind turbine of  claim 39 , wherein each transmitter transmits light having a unique frequency or a unique range of frequencies that is different to the frequencies transmitted by the other transmitters. 
     
     
       41. The wind turbine of  claim 39 , wherein each transmitter transmits light having a unique polarisation that is different to the polarisation of light transmitted by the other transmitters.